This project has investigated communication by facial expressions, hand gestures, and body postures in rhesus, pigtail, and stumptail macaques. Specifically, this project has investigated both how the social environment typical of each species affects communication patterns and the cognitive processes involved in gestural communication. The dataset for this project included 300 hours of observation of one social group of each species. The three species differ significantly in the size of the gestural repertoire and in the complexity of communicative interactions. These differences can be accounted for, at least in part, by the influence of dominance and kinship on social interactions in the three species. Although macaques engage in complex exchanges of information through gestural signals, there is no evidence that they possess the ability to attribute knowledge or mental states to other individuals. This project has enhanced our knowledge of the communicative and cognitive abilities of macaques and our understanding of the relation between social environment and communication systems in primates. Moreover, the comparative data from macaques have provided some insight into the role of gestural communication in language evolution.